1. Field of the Invention
This invention relates to the field of paper and, more particularly, to perforated sheets for sheets, pads, and form-sets of paper and carbonless paper.
2. Description of the Related Art
Carbonless copy paper is capable of producing an image upon application of pressure and generally involves coating a reactant, such as a color-former, on one substrate, and a co-reactant, such as a developer, on a second mating substrate. Separation and prevention of premature reaction of the reactants is accomplished by encapsulation of one of the reactants. The color-former is a color-forming compound that is contained or encapsulated in microcapsules on one sheet of paper. The co-reactant (the developer) is carried on a mating sheet of paper. The microcapsules thereafter isolate the two co-reactants until such time as pressure is applied to the paper, thereby breaking the microcapsules for the purpose of creating an image.
A common construction comprises encapsulated color-formers dissolved in an appropriate solvent, and coated onto the back side of a donor sheet in a suitable binder, referred to as a "coated back" (CB) sheet. The term "suitable binder" refers to a material, such as starch or latex, that allows for dispersion of the reactants in a coating on a substrate, and is readily rupturable under hand-held stylus pressure, or typical business machine key pressure. The developer, optionally in a suitable binder, is coated onto the front side of a mating or receptor sheet, referred to as a "coated front" (CF) sheet. When activating pressure is applied to the face of the donor sheet, the capsules rupture and release the color-former for transfer to the receptor sheet, thus forming a colored pattern due to the reaction between the color-former and developer. Such a construction is known as a "form-set" construction.
Constructions also include substrates with one surface coated with an encapsulated color-former, and a second, opposite, surface on which is coated a developer. Such sheets are generally referred to as "CFB" sheets (i.e., coated front and back sheets). CFB sheets can be placed between CF and CB sheets to provide a construction involving a plurality of substrates. Each side, including color-former thereon, should be placed in juxtaposition with a sheet having a developer thereon. CFB sheets are also typically used in form-sets. In some applications, multiple CFB sheets have been used in form-sets.
An alternative to the use of CB, CF, and CFB sheets is a self-contained carbonless paper in which both the color-former and developer are applied to the same side of a sheet and are incorporated into the fiber lattice of a paper sheet.
In one commercial product, microcapsules on the donor sheet contain dithiooxamide (DTO) derivatives, and the receptor sheet is coated with selected salts of nickel. When the two coated faces are contacted such that the derivatives and the metal salt can combine and react, a coordination complex forms and an image results. Typically, this occurs by transfer of the derivative to the site of the metal salt, i.e., transfer of the derivative from the donor sheet to the receptor sheet. The image thereafter forms on the receptor sheet.
Carbonless papers are widely used in the forms industry and form-sets are often prepared by collating from about two to eight sheets of carbonless paper. Pads are often prepared by edge-padding or gluing the edges of a stack of form-sets. Each of the coated sheets in a form-set is somewhat porous and permits the adhesive to penetrate into the pores of the paper, such penetration being necessary to attain satisfactory adhesion. By tearing along the adhesively bound edge, the sheets of a form-set are separated.
"Fan-apart" is a method of separating a stack or pad of multiple form-sets into individual sets. One method of "fan-apart" involves a stack of collated sheets being gripped at the edge-padded end of the stack with one hand and the unpadded end with the other, and bending the stack into a "U" shape. While holding the stack horizontally, the padded end is released and allowed to droop downward. This provides enough stress on the adhesive to separate the pad or stack into individual form-sets.
Carbonless copy paper form-sets often have a coating (such as a fluorocarbon coating) on at least one of the outer faces of each form-set. Fluorocarbon coatings provide low adhesion properties to the outer faces of the pad and promote the "fan-apart properties" in the edge padding. In collated carbonless copy papers currently on the market, at least one of the outer faces of each form-set typically has been treated with a silicone, fluorocarbon, or some other coating which counteracts curling that otherwise would result from the functional coating on the other surface of that sheet. The low adhesion coating also acts as a release agent for the edge-padding adhesive such that the adhesively edge-padded stack can "fan-apart" and separate into individual form-sets.
Perforation of each sheet of a form-set is often desired. In use, the individual sheets of the padded form-set are separated by tearing along the perforation. Typically, the edges of the form-set are perforated, affording a form portion and an edge or tab portion. Such constructions are known as snap-out or uni-set forms. An apparatus for perforating sheet material is disclosed by W. H. Harding in U.S. Pat. No. 3,226,527.
The method currently used to perforate carbonless paper is mechanical perforation. However, this method has not been completely satisfactory. Mechanical perforation of the carbonless paper ruptures some microcapsules with resultant staining around the perforations. Furthermore, mechanical perforation in either carbonless paper or regular paper scores and weakens the paper along the row of perforations, thus leading to a weakened perforation area which may prematurely release. Another problem encountered with mechanical perforation includes the presence of a burr left on the paper such that a stack of the perforated paper is thicker in the perforated region due to the burred areas, and thus the stack does not lie flat. Attempts to remove these burrs leads to removal of the paper coatings necessary for proper development of images on carbonless paper and adds another expensive step to processing either carbonless paper or regular paper. Another disadvantage of mechanical perforation includes the accumulation of lint and paper dust around the punched holes, which often clings to the form set and must be manually removed.
Carbonless paper may be perforated either before, after, or as the forms are printed, using either a lithographic press, an offset press, or a perforating machine.
Perforating can be carried out on a lithographic press either before or after printing by using a material known as perforating tape, a narrow piece of metal with upraised spikes which is attached to the impression roll of the press. Feeding of the paper through the press thus results in impingement of the perforating tape on the paper. However, because of the construction of the lithographic press, the rotation of the impression roll also results in impingement of the perforating tape on the rubber blanket roll, resulting in perforation and consequent destruction of the blanket. The printer must therefore allow for the cost of replacement of the blanket when figuring the cost of the job. This two-step operation requires additional time and expense on the part of the printer.
As discussed previously, if paper is perforated by any of the above methods prior to printing,.the burr of paper detritus on the paper thickens the paper stack in the region of perforation. The resulting stack does not lie flat and subsequent attempts to stack such pre-perforated paper in a printing press or copy machine often results in jamming of the paper feed apparatus, causing ruined sheets. Gripping of the perforated edge of the paper during the feed step of printing or duplicating can also result in premature tearing of the paper along the perforation. The press or copy machine thus needs to be closely monitored to prevent jamming and overflow in the receiving tray.
An additional problem results when the carbonless paper is mechanically perforated. Mechanical perforation of the collated paper, at any stage in form-set production, results in capsule rupture and transfer of the color-former from the CB sheet to the developer sheet. As a result, an unsightly line forms along the line of perforation and also occurs in regions adjacent the perforation.
To compensate for the losses of carbonless paper sheets during the perforation processes presently employed, additional paper must be used to assure that the required number of acceptable form-sets have been prepared at the end of the printing job. This additional press run can require up to 10% more paper being used and also adversely effects the productivity of the printing operation.
For the above-mentioned reasons, it is difficult to prepare perforated pads and form-sets employing carbonless paper, and to prepare paper having a perforation that is suitable for feeding through sheet-fed equipment. It would be desirable to have a method of perforating paper which would provide sheets which lay flat, can be easily packaged, boxed and shipped, are easy to print and pad and, in the case of carbonless paper, do not have any staining resulting from premature capsule rupture. Heretofore there has been no method of perforating paper that meets these objectives.